There have been proposed so far a variety of Drop-On-Demand ink-jet recording heads. One known method for reproducing a continuous halftone image by use of the ink-jet recording head is to deposit large and small ink droplets onto a recording medium. For this purpose, large-diameter nozzles and small-diameter nozzles whose sizes are different from each other are provided for the head to achieve a gradation reproduction by suitably ejecting large and small ink droplets through the large-diameter and small-diameter nozzles, respectively, in response to image signals.
However, a wide range of gradation cannot be achieved simply by providing different diameters for respective nozzles, and a smooth halftone image like a photograph can not be reproduced.
Also, in order to form nozzles having different diameters in a head plate by laser beam machining, the diameter of the laser beam must be changed in accordance with the desired diameters. Instead, when forming the nozzles by drilling, various size of drills and corresponding tools must be prepared and further they must be exchanged depending upon the sizes of the desired diameters. Therefore, forming nozzles of different diameters has been a very complicated and inefficient approach.